MathDB
Number of permutations

Source: Baltic Way 2014, Problem 7

November 11, 2014
combinatorics proposedcombinatorics

Problem Statement

Let p1,p2,...,p30p_1, p_2, . . . , p_{30} be a permutation of the numbers 1,2,...,30.1, 2, . . . , 30. For how many permutations does the equality ∑k=130∣pk−k∣=450\sum^{30}_{k=1}|p_k - k| = 450 hold?
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